1. Field of the Invention
The present invention relates to a semiconductor device manufacturing method and a semiconductor manufacturing apparatus, and more particularly, to a semiconductor device manufacturing method including a silicon nitride film manufacturing step using a thermal CVD (Chemical Vapor Deposition) method or a silicon oxynitride film manufacturing step using a thermal CVD method, and to a semiconductor manufacturing apparatus preferably used for the method.
2. Description of the Related Art
Conventionally, it is common that a silicon nitride film used in a semiconductor device is formed using mixed gas of SiH2Cl2 (DCS, hereinafter) and NH3 and that a silicon oxynitride film used in a semiconductor device is formed using mixed gas of DCS, NH3 and N2O.
According to this method, however, it is necessary to form the silicon nitride film at a temperature as high as 700xc2x0 C. to 800xc2x0 C. and as a result, there is a problem that impurities are adversely diffused deeply into a shallow diffused layer and a semiconductor device element can not be formed small in size. Further, there is a problem that NH4Cl (ammonium chloride), which is a by-product of reaction, adheres to a discharge port, this NH4Cl generates rust on a metal surface, and metal contamination is generated on a semiconductor wafer.
To solve the problems, the present inventors examined forming a silicon nitride (Si3N4) film using NH3 and SiH2(NH(C4H9))2(bis tertiary butyl amino silane: BTBAS, hereinafter) as raw gases and forming a silicon oxynitride (SiON) film using BTBAS, NH3 and N2O as raw gases. As a result, the inventors have found that the silicon nitride film and the silicon oxynitride film can be formed at a low temperature of about 600xc2x0 C. and NH4Cl, which is a cause of metal contamination, is not generated.
The present inventors, however, have found that when a silicon nitride film or a silicon oxynitride film is formed using BTBAS, uniformity in thickness of the formed film over the entire surface of the substrate is not sufficient.
FIG. 1 shows a structure of a furnace used when a silicon nitride film is formed using BTBAS and NH3 as raw gases, and when a silicon oxynitride film is formed using BTBAS, NH3 and N2O as raw gases.
A case in which the silicon nitride film is formed using BTBAS and NH3 as raw gases will be explained as one example.
A quartz reaction tube (outer tube) 11 is located outside, and a cylindrical quartz inner tube 12 is disposed inside of the quartz reaction tube 11. A quartz boat 14 is disposed inside of the quartz inner tube 12. The quartz boat 14 supports a large number of semiconductor wafers 16.
BTBAS and NH3 are introduced into a furnace through quartz nozzles 21 and 18, respectively. The gases are first introduced into the quartz inner tube 12 and flow from below upward. The gases are discharged out from the quartz inner tube 12 from above downward.
BTBAS and NH3 decompose by heat during this process forming Si3N4 on the semiconductor wafer 16 and a quartz surface.
FIG. 4A shows a schematic transversal sectional view of the quartz inner tube 12 and its interior, and FIG. 4B is a schematic longitudinal sectional view thereof.
The present inventors first formed a silicon nitride film using BTBAS and NH3 as raw gases having the same compositions as those used for other raw gases.
The plurality of semiconductor wafers 16 each having a diameter of 200 mm were stacked by boat columns 25 in the vertical direction in the quartz inner tube 12 having an inner diameter of 260 mm, and films were formed. A distance xe2x80x9cbxe2x80x9d between edges of the semiconductor wafers 16 and an inner wall of the quartz inner tube 12 was 30 mm. A distance xe2x80x9caxe2x80x9d between the adjacent semiconductor wafers 16 was 6.35 mm.
As a result, a thickness of the Si3N4 film was thin around a peripheral portion of the wafer, and the film at the central portion of the wafer was thin and reentrant in shape. When the silicon oxynitride film was formed using BTBAS, NH3 and N2O as raw gases, the same result was obtained.
Thereupon, the present invention provides a semiconductor device manufacturing method and a semiconductor manufacturing apparatus in which when a silicon nitride film is formed using BTBAS and NH3 as raw gases, and when a silicon oxynitride film is formed using BTBAS, NH3 and N2O as raw gases, the uniformity in thickness of the formed film over the entire surface of the substrate can be enhanced.
The present inventors have considered that at the center portion of a semiconductor wafer 16, because other semiconductor wafers 16 are located below and above the semiconductor wafer, space in the vicinity of the semiconductor wafer is small, but at the peripheral portion of the semiconductor wafer, a large space exists between the semiconductor wafer and the quartz inner tube 12, and therefore, the film formed on the semiconductor wafer is thick at the peripheral portion of the semiconductor wafer and is thin and reentrant in shape at the central portion of the semiconductor wafer. Following the above-mentioned consideration, the present inventors have studied a relation of relative values between the distance xe2x80x9caxe2x80x9d between the adjacent semiconductor wafers 16 and the distance xe2x80x9cbxe2x80x9d between the edge of the semiconductor wafer 16 and the quartz inner tube 12, to distribution of a thickness of a film formed on the semiconductor wafer 16 over the entire surface of the wafer 16, and as a result, the present inventors have reached the present invention.
According to a first aspect of the present invention, there is provided a semiconductor manufacturing apparatus which forms silicon nitride films on a plurality of substrates by thermal chemical vapor deposition, including:
a vertical reaction tube having an inner wall;
a substrate holder which is to hold the plurality of substrates in the vertical reaction tube with the plurality of substrates being vertically stacked, a distance xe2x80x9caxe2x80x9d between adjacent substrates of the plurality of substrates and a distance xe2x80x9cbxe2x80x9d between edges of the plurality of substrates and the inner wall of the vertical reaction tube being maintained substantially equal to each other; and
gas supplies which supply bis tertiary butyl amino silane and NH3 into the vertical reaction tube such that the bis tertiary butyl amino silane and the NH3 flow vertically from one end of the plurality of substrates to an opposing end of the plurality of substrates and do not flow into the vertical reaction tube through the inner wall at a height between the one end and the opposing end of the plurality of substrates, to form the silicon nitride films on the plurality of substrates.
Preferably, a value of a ratio xe2x80x9cb/axe2x80x9d, which is a ratio of the distance xe2x80x9cbxe2x80x9d between the edges of the plurality of substrates and the inner wall of the vertical reaction tube to the distance xe2x80x9caxe2x80x9d between the adjacent substrates, is set to be in a range of 0.5 to 1.1.
According to a second aspect of the present invention, there is provided a semiconductor manufacturing apparatus which forms silicon oxynitride films on a plurality of substrates by thermal chemical vapor deposition, including:
a vertical reaction tube having an inner wall;
a substrate holder which is to hold the plurality of substrates in the vertical reaction tube with the plurality of substrates being vertically stacked, a distance a between adjacent substrates of the plurality of substrates and a distance xe2x80x9cbxe2x80x9d between edges of the plurality of substrates and the inner wall of the vertical reaction tube being maintained substantially equal to each other; and
gas supplies which supply bis tertiary butyl amino silane, NH3 and N2O into the vertical reaction tube such that the bis tertiary butyl amino silane, the NH3 and the N2O flow vertically from one end of the plurality of substrates to an opposing end of the plurality of substrates and do not flow into the vertical reaction tube through the inner wall at a height between the one end and the opposing end of the plurality of substrates, to form the silicon oxynitride films on the plurality of substrates.
Preferably, a value of a ratio xe2x80x9cb/axe2x80x9d, which is a ratio of the distance xe2x80x9cbxe2x80x9d between the edges of the plurality of substrates and the inner wall of the vertical reaction tube to the distance xe2x80x9caxe2x80x9d between the adjacent substrates, is set to be in a range of 0.5 to 1.1.
According to a third aspect of the present invention, there is provided a semiconductor device manufacturing apparatus, which forms silicon nitride films on a plurality of substrates by thermal chemical vapor deposition, including:
a boat which has a boat column and which is to hold the plurality of substrates with the plurality of substrates being stacked on the boat;
a reaction tube which is to accommodate the boat and the plurality of substrates stacked on the boat and which is provided at a position corresponding to the boat column, with a boat column groove for accepting the boat column; and
gas supplies which supply bis tertiary butyl amino silane and NH3 into the vertical reaction tube, wherein
a distance xe2x80x9caxe2x80x9d between adjacent substrates of the plurality of substrates and a distance xe2x80x9cbxe2x80x9d between edges of the plurality of substrates and an inner wall of the reaction tube are maintained substantially equal to each other.
According to a fourth aspect of the present invention, there is provided a semiconductor device manufacturing apparatus, which forms silicon oxynitride films on a plurality of substrates by thermal chemical vapor deposition, including:
a boat which has a boat column and which is to hold the plurality of substrates with the plurality of substrates being stacked on the boat;
a reaction tube which is to accommodate the boat and the plurality of substrates stacked on the boat and which is provided at a position corresponding to the boat column, with a boat column groove for accepting the boat column; and
gas supplies which supply bis tertiary butyl amino silane, NH3 and N2O into the vertical reaction tube, wherein
a distance xe2x80x9caxe2x80x9d between adjacent substrates of the plurality of substrates and a distance xe2x80x9cbxe2x80x9d between edges of the plurality of substrates and an inner wall of the reaction tube are maintained substantially equal to each other.